The "Toffee Apple" nickname derives from the power handle, which was detachable, and looked like a toffee apple, especially when hand held after it had been detached. Only the 20 pilot scheme Brush Type 2s, which had electro-magnetic control, had that type of power handle, so the 20 pilot scheme locos are also usually referred to as Toffee Apples.
Electrification warning flashes and coupling codes both predate blue livery. The blue livery on 31018 should have both, but has neither. 31018 has been like that since it was repainted blue at York more than 20 years ago. That followed a period of about 25 years in green livery, painted at Doncaster Works prior to being handed over to the National Railway Museum.